1. Field of the Invention
The present invention relates, in general, to spindle motors and, more particularly, to an ultra-slim spindle motor, which has a reduced thickness because the production tolerance and/or the assembly tolerance are reduced.
2. Description of the Related Art
Generally, spindle motors are provided therein with hydrodynamic bearings for producing hydrodynamic pressure, and are preferably used in drive devices, such as hard disc drives (HDD). In recent years, spindle motors have come to be used in highly portable products, such as MP3 players or mobile phones, and thus it is required to accomplish compactness, smallness, lightness and/or thinness of the spindle motors. An example of conventional spindle motors is shown in FIG. 8 and FIG. 9.
As shown in FIG. 8 and FIG. 9, the conventional spindle motor 800 comprises a fixed assembly 810 and a rotary assembly 850, which is rotatably supported on the fixed assembly 810.
The fixed assembly 810 comprises a base 811, a bearing holder 813, a bearing 815, a sealing cap 817, an armature 819, a thrust washer 821 and a thrust washer support plate 823.
The base 811 is securely mounted to a drive device (not shown), such as a hard disc drive (HDD) in which the spindle motor 800 is installed. A central opening 812 is formed through the center of the base 811.
The bearing holder 813 is inserted into the central opening 812 and is caulked to the base 811 at the lower end thereof. The bearing 815 is fitted into the bearing holder 813 such that the central axis thereof is aligned with the central axis of the rotating shaft 851, and the outer surface thereof is in close contact with the inner circumferential surface of the bearing holder 813.
The sealing cap 817 is inserted into the bearing holder 813 such that it is secured to the inner circumferential surface of the bearing holder 813 and closes almost all of the lower end of the bearing 815 at a location below the bearing 815. The armature 819 is securely installed on the outer circumferential surface of the bearing holder 813.
The thrust washer 821 is inserted into the bearing holder 813 and is secured to the inner circumferential surface of the bearing holder 813, such that the washer 821 is in contact with the lower end of the rotating shaft 851. The thrust washer support plate 823 is inserted into the bearing holder 813 and is secured to the inner circumferential surface of the bearing holder 813 such that the support plate 823 is in contact with the lower surface of the thrust washer 821. In the above state, the thrust washer support plate 823 is secured to the bearing holder 813 by caulking the bearing holder 813.
Here, as shown in FIG. 10, to mount the thrust washer 821, the base 811 is seated on an assembly jig 80 such that both the bearing 815 and the bearing holder 813 are inserted into a depression 81 of the assembly jig 80 and, thereafter, the thrust washer 821 is inserted into the bearing holder 813 by forcing the thrust washer 821 in the direction shown by the arrow in FIG. 10.
The rotary assembly 850 comprises a rotating shaft 851, a rotor cover 853, a magnet 855 and a rubber turntable 857.
The rotating shaft 851 is supported at the lower end thereof by the thrust washer 821 in a thrusting direction. The outer circumferential surface of the rotating shaft 851 is rotatably supported by the bearing 815 in a non-contact method. The rotor cover 853 is secured to the upper end of the rotating shaft 851.
The magnet 855 is secured to the inner circumferential surface of the rotor cover 853 such that the magnet 855 faces the armature 819. The rubber turntable 857 is secured along the outer edge of the upper surface of the rotor cover 853.
In the above-mentioned construction, the height of the spindle motor 800 is determined by the height H from the upper surface of the base 811 to the upper surface of the rubber turntable 857. Thus, the height of the spindle motor 800 can be reduced by reducing the height H from the upper surface of the base 811 to the upper end of the rubber turntable 857. The height H is determined by the difference between the height h1 from the upper surface of the thrust washer 821 to the upper surface of the rubber turntable 857 and by the height h2 from the upper surface of the base 811 to the upper surface of the thrust washer 821. That is, H=h1−h2. Further, as shown in FIG. 10, the height h2 from the upper surface of the thrust washer 821 to the upper surface of the base 811 is determined by the difference between the thickness h4 of the base 811 and the thickness h3 of the thrust washer 821, that is, h2=h4−h3.
Here, the thicknesses h4 and h3 are determined in consideration of tolerance during a process of producing the base 811 and the thrust washer 821. The tolerance, which is considered during the determination of h4 and h3, is the production tolerance of h2. Further, the thickness h1 is determined in consideration of tolerance during a process of producing the rubber turntable 857. The tolerance, which is considered during the determination of h1, is the tolerance of the height H of the spindle motor during the process of assembling the elements into the spindle motor 800. Thus, when the elements are completely assembled into the spindle motor 800, a large accumulated tolerance may result, reducing the reliability of the size of the product and making it difficult to realize a compact product.
Further, the contact ends of the assembly jig 80, which is used for pressure-fitting the thrust washer 821, have different heights, in other words, the central contact end 82 and the outside contact end 83 of the assembly jig 821 have different heights, so that the contact ends 82 and 83 require separate cutting operations, such as planing or grinding operations. Thus, it is difficult to produce the assembly jig 80.